Chemical weapons have been used on a wide scale in the Syria war and there is clear evidence sarin killed hundreds in one key attack, UN inspectors say.
"The conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic ... against civilians, including children, on a relatively large scale," says the report to be released by UN leader Ban Ki-moon on Monday.
The report said there was "clear and convincing" evidence of the use of sarin gas in an attack near Damascus last month.
The United States says 1400 people died in the attack.
It added that "surface-to-surface rockets containing the nerve agent sarin were used" in the August 21 attack.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The detail was in the first page of the report which was inadvertently leaked when it was included in an official picture of UN investigation leader Ake Sellstrom handing over the report to UN leader Ban Ki-moon.
Ban was to give the full report to the UN Security Council on Monday.
The United States, Britain and France blame President Bashar al-Assad's forces for the attack east of Damascus on August 21.
The government, backed by Russia, denies the charge and blames opposition rebels.
